Within control systems, there has a need to make I/O devices and modules, programmable logic controllers (PLCs), and other devices capable of being used on standard communications protocols, such as Ethernet, TCP/IP, and others. This includes the ability to interface a proprietary communications protocol with standard protocols. Previous I/O scanners within such devices, typically used proprietary control networking protocols. Using proprietary control networking protocols, resulted in high installation costs, low ease-of-use, and compatibility problems with other devices/systems used in control systems, such as in factory automation applications. U.S. Pat. Nos. 5,159,673 (Sackman et al.), 4,992,926 (Janke et al.), 4,897,777 (Jamke et al.), 5,245,704 (Weber et al.), 4,937,777 (Flood et al.), 5,307,463 (Hyatt et al.), and/or 5,805,442 (Crater et al.) provide some background and context for the present invention.
PLCs have been implemented in duplex or back-up system configurations for several years. Typically, the duplex configuration incorporates a pair of PLCs assembled in a hot or active standby, or back-up, configuration wherein one PLC is operating in a primary mode and the other PLC is functioning in a secondary or standby/backup mode. System failures involving the primary mode PLC that can shut down the control system are avoided by having a back-up PLC readily available in hot/active standby mode to replace the failing primary mode PLC.
Factory automation systems are increasingly being integrated with communication networks. Control systems are being implemented on networks for remote monitoring and control of devices, processes, etc. Signal communication between devices on a network requires network address identifiers, i.e., Internet Protocol address, Media Access Control address; to be assigned to these devices throughout the network.
Network problems arise when a device or PLC fails and must be replaced. The failing network PLC cannot be readily exchanged with a PLC configured in active standby because the network address identifier assigned to the PLC to be removed is not readily associated with the active standby PLC.
The present invention is provided to solve these and other problems.